The present invention relates to a driver assistance system for a vehicle adapted to assist the driver in controlling the direction of a moving vehicle along a predetermined path.
Lane following systems have been demonstrated operating at motorway speeds. Such systems certainly prevent lane departure while lane markings are present. According to a known system, a contrived centerline between lane markings of a road is tracked and a steering bias is applied to a steering system of a vehicle in such a manner as to assist the driver in tracking the contrived centerline position. The contrived centerline may be a true centerline between lane markings, for example on a motorway, or may be offset from the true centerline to facilitate the negotiation of curves. The steering bias is a torque input to the steering, which may either assist or oppose the steering torque from the driver. A camera or equivalent sensor is mounted on the vehicle and used to detect the lane markings on the road. An associated signal processor estimates the vehicle""s lateral position in relation to the lane markings. The vehicle""s lateral position may be a vehicle""s lateral displacement from the contrived centerline or from a boundary of a lane defined by the line markings. An actuator, which may take the form of an electric motor, coupled to the steering mechanism is used to provide a torque input to the steering. The processor is designed to assist the driver to maintain the vehicle""s lane position by preventing lane departure using a biasing torque.
The steering mechanism has friction that affects a ratio between the ampere of electric current input passing through the electric motor and the magnitude of torque output, which may be used as a steering bias. The greater the friction, the less the torque is. With the same ampere of electric current, variation in friction, which may be found even among production units of a steering mechanism of the same type may cause variation in torque used as steering bias. In a production unit of steering mechanism, friction is not constant over the whole period of its service life. Usually, friction drops after extended period of use. Accordingly, a need remains to adjust or regulate the ampere of electric current to provide torque acceptable by a driver against variation in friction in steering mechanism. Initial adjustment of setting of gain on product-by-product basis and/or the subsequent readjustment in each product would be required due to difficulties in achieving adaptive control of gain needed to cope with friction in steering mechanism.
It is therefore an object of the present invention to provide a method or a system for assisting a driver in tracking a contrived centerline between lane markings on a road, which does not require initial adjustment on product-by-product basis to cope with variation in friction in steering mechanism and the subsequent readjustment in each product.
According to one aspect of the present invention, there is provided a method of assisting a driver of a vehicle in tracking a contrived centerline between lane markings defining a lane boundary on a road by applying a steering bias to a steering system of the vehicle, the steering system being provided with an actuator, which provides the steering bias in response to an estimate produced by an observer that has a friction term correlated with friction in the steering system, the method comprising:
establishing an ideal frequency function of lateral displacement data;
sampling lateral displacement of the vehicle in relation to the lane markings to provide a real frequency function of lateral displacement data;
comparing the real frequency function with the ideal frequency function; and
updating or leaving unaltered the friction term based on the result of comparison.
According to another aspect of the present invention, there is provided a driver assistance system for a vehicle adapted to assist a driver in tracking a contrived centerline between lane markings defining a lane boundary on a road by applying a steering bias to a steering system of the vehicle, the steering system being provided with an actuator, which provides the steering bias in response to an estimate produced by an observer that has a friction term correlated with friction in the steering system, the system comprising:
a lane recognition unit providing a lateral displacement of the vehicle in relation to the lane markings; and
a controller;
a computer readable storage media having data representing instructions executable by the controller, the computer readable storage media having:
instructions for establishing an ideal frequency function of lateral displacement data;
instructions for sampling the lateral displacement of the vehicle in relation to the lane markings to provide a real frequency function of lateral displacement data;
instructions for comparing the real frequency function with the ideal frequency function; and
instructions for updating or leaving unaltered the friction term based on the result of comparison.